This invention generally relates to an apparatus and method for coating articles. More specifically, the invention provides either a liquid or melted powder coating to the head/shank junction of externally threaded fasteners.
There are many fastener applications that require a coating, such as a sealant coating, to be applied over the head/shank junction of male fasteners. For example, externally threaded fastener 12 shown in FIG. 6 includes head 13 and shank 18, and knurls 16 at the head/shank junction which extend generally normal to threads 17 on shank 18. Knurls 16 can then be coated with a suitable coating 19, as shown in FIG. 7, and coated fastener 12 can be put to a variety of uses. As one example, coated fastener 12 can then be pressed into an aperture within a stamping, to provide a mechanical lock within the stamping using coated knurls 16.
Various apparatus and methods are known for applying coatings to fasteners. For example, U.S. Pat. No. 4,842,890 discloses a powder spray apparatus which employs oppositely-directed belts to rotate the fasteners during spraying, while U.S. Pat. No. 4,775,555 patent describes relatively accurate spraying of internally threaded fasteners to provide a self-locking patch. U.S. Pat. Nos. 5,078,083 and 5,090,355 disclose rotating magnetic means for holding and rotating fasteners during spraying. However, the prior art fails to teach the application of a closely defined and substantially uniform coating to a specific location on an externally threaded fastener, such as the head-shank junction, for predetermined, intermittent time periods, with the coating application being responsive to fastener movement.